1. Field of the Invention
The present invention relates to a method of machining an impeller, in which a cutting work can be performed with high efficiency, an impeller, and an impeller cutting jig.
2. Description of the Related Art
In recent years, a case where an impeller to be used in an automobile or an air conditioner is shaped using a cutting work is increasing. In a cutting work of the impeller, there are many cases of using a cutting tool having a large diameter or increasing a cutting speed so as to efficiently perform the cutting work and to shorten machining time, in particular, at a stage of rough work prior to a finish work. In order to use the cutting tool having a large diameter or increase the cutting speed in the cutting work of the impeller, it is necessary to fix a workpiece to a cutting jig in a way to withstand a large cutting load.
Japanese Patent Application Laid-Open No. 2011-513077 discloses a technique in which a workpiece is placed on a cutting jig, the workpiece is pressed against the jig from the top in an axial direction of a hole formed in a central part of the workpiece, and then the workpiece is fixed to the jig. In this technique, preferably, the workpiece is pressed against the jig over a wide range in order to firmly fix the workpiece to the jig.
However, in general, an upper part of the impeller (workpiece) has a wide machining range in many cases. If the workpiece is pressed over the wide range, possibly the cutting tool for machining interferes with the jig.
On the contrary, in order to avoid the interference between the cutting tool and the jig, when the workpiece is pressed in a narrow range near the center, there is a concern that rotational deviation may occur in the workpiece due to the cutting load, a machining defect of the workpiece may occur due to influence of the rotational deviation, or a damage to the cutting tool may occur. Therefore, in order to prevent the occurrence of the rotational deviation, there is a method of decreasing a machining speed or increasing a pressing force from the top.
However, when the machining speed is decreased, the machining requires much time and thus machining efficiency is reduced. In addition, there is a limitation in increasing the pressing force from the top, and when the pressing force is forcibly increased, there is also a concern that unexpected deformation of the workpiece may occur or desired performance of the impeller may not be obtained.